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1.10 MOD Unit 1 Assessment: Twins with Different Skin Color

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You can also watch the recording of our Unit 1 Review where we covered all of the concepts found here.

Meet the 11-year-old twins with two different skin tones.

There's no trouble telling these 11-year-old twins apart, as one is white and one is black. Marcia and Millie Biggs looked almost identical when they were born but their difference in skin tone became more apparent as they aged. As brown-eyed Millie started to become darker skinned, blue-eyed Marcia took on a lighter complexion and grew blonde, curly hair. The twins' mom is white, while their dad is Jamaican.

The image shows the UK family from the video. The image includes (from left to right) Mom, Millie, Marcia, and Dad. Millie and Marcia are twins; they were born from the same parents at the same time.

Table 1 shows the genotypes for the different observable phenotypes of skin color.

Question 1

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Question 2

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3.

Figure 1 shows a biological process that occurs during sexual reproduction.

Question 4

4.

Using Figure 1, provide a biological explanation that includes reasoning for the genetic variation between the twins.

Marcia and Millie enjoy a weekend at the beach with their parents.  Everyone had a fun time, but when they got home, Marcia’s skin was red and very uncomfortable for a few days.

Question 5

5.

The image shows the effect of UV photons (sunlight) on DNA.

Question 6

6.

Using the image above, give a scientific explanation of Marcia's sunburn that supports the claim above.

As the twins got older, their mother was diagnosed with breast cancer. Mom took the test to find out if she carried the breast cancer gene (BRCA1). 

The test came back negative. In addition to lacking the breast cancer gene, Marcia and Millie’s mother had not been exposed to any carcinogens.

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Question 8

8.

Give a scientific explanation of twin's mom's cancer that supports the claim above.

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Which topics were difficult for you and which did you find most interesting?

If Marcia and Millie's mother had the very light skin phenotype (aabbCc genotype), which of the following combination of alleles could she have given her daughters?  

Abc

abC

aBC

If Marcia and Millie's father had the dark skin phenotype (AaBbCC genotype), which of the following combination of alleles could he have given his daughters?  Select all possibilities. (Hint use FOIL method)

aBC

abC

AbC

aBc

Based on the evidence from the video and images, make a claim: Millie and Marcia have different skin colors, even though they have the same parents, as a result of...

new genetic combinations through meiosis

viable errors occurring during DNA replication

mutations caused by environmental factors

Based on the evidence from the video and images, make a claim: Marica's sunburn is a result of...

new genetic combinations through meiosis

viable errors occurring during DNA replication

mutations caused by environmental factors

Based on the given information, make a claim: The twins' mom's cancer is a result of...

new genetic combinations through meiosis

viable errors occurring during DNA replication

mutations caused by environmental factors

What is the gene pool?

An individual's inherited traits.

The total genes in a population.

The genes of an individual.

What is the source of genetic variation?

Mutation and recombination

Natural selection

Genetic drift

What is genetic variation?

Genetic diversity in a population

Physical traits

Inherited diseases

Where did the alleles for antibiotic resistance come from?

Genetic recombination

Mutations in DNA

Environmental factors

What is the term for the introduction of new genes in a population?

Gene flow

Genetic drift

Gene mutation

Which factor causes genetic drift?

Chance events

Migration

Mutation

Why is variation in populations important for species survival?

Fewer traits help populations stay stable

Increases likelihood of adapting to changing conditions

Decreases competition

What does allele frequency refer to?

The rate at which cells undergo mitosis and meiosis.

The number of chromosomes in a haploid cell.

The occurrence of a specific version of a gene in a population.